The present invention relates to a roller, particularly a hot roller, which is reinforced with a working jacket of a hard metal or the like, and particularly a roller in which the working jacket is prestressed by a compression pressure applied in the direction of the longitudinal axis of the roller via clamping rings which have clamping surfaces that are arranged at an angle with respect to the roller body.
In the case of many types of rollers, particularly hot profile rollers, there has been in recent times a demand for structures capable of supporting ever higher specific surface stresses. As a result, the use of rollers made of conventional materials, i.e. steel or heat resisting steel and the like has become more and more uneconomical.
To overcome this drawback, such rollers have been given surface reinforcements which are capable of withstanding greater stresses, in particular hard metal reinforcements. In special cases the hard metal can be replaced by special heat resistant alloys, sintered metals or other suitable materials.
Such reinforced rollers are disclosed, for example, in German Offenlegungsschrift [Laid-Open Application] No. 1,427,871. They include a roller core of steel or the like onto which is placed a roller body of a hard metal, hard-cast, or the like material which is clamped in between suitable abutments or clamping rings to maintain a permanent pressing force acting in the direction of the longitudinal axis. With such an arrangement the roller body is protected against wear, breaks and the like, and serves substantially to transfer the rotating moment to the working jacket. In such an arrangement, the roller pressure is transferred to the roller body, which is made to be elastic to the extent that it is capable of absorbing bending stresses. According to a particular embodiment, the clamping surfaces of the device are inclined toward the roller core so that the pressure force has a centripetal component directed toward the roller core.
Reinforced rollers of this type are satisfactory in practice if the prevailing operating temperatures do not get too high. At higher operating temperatures they have the drawback that the radial stress exerted by the roller body on the working jacket can cause the latter to burst. The reason for this is that the coefficients of linear thermal expansion of the steels usable for this purpose are approximately three times greater than the coefficients of linear thermal expansion of the conventional hard metals. As a basis for discussion, it can be assumed that the coefficient of linear thermal expansion of steel is about 13-18 .multidot. 10.sup.-6 .multidot. degree .sup.-1 and that of hard metal about 5-7.multidot.5 .multidot. 10.sup.-6 .multidot. degree .sup.-1 . Unfortunately there is the added fact that hard metal is capable of absorbing extraordinarily high friction and pressure stresses but, as a result of its relatively soft cobalt matrix, is less able to withstand tensile stresses.